It can be any of the three, and sometimes a combination. The way to find out is to reproduce the cracking under controlled conditions, so you are comparing evidence rather than opinions. Start from what you have: retained samples from the same production lot, the returned garments, and the factory's print process records.

Reproduce it with a controlled wash

Wash retained, unworn hoodies from the same lot under a named home-laundering procedure such as ISO 6330, following your care label, for an agreed number of cycles. If retained samples crack under the labelled care, the problem is in the product, not in how customers washed it. If they do not crack, compare them closely with the returns. Look for signs of harsher treatment, but also for differences in lot, colour or print position.

Note that colour-fastness methods such as ISO 105-C06 assess colour change and staining from laundering. They are useful for colour complaints, but cracking is a physical failure of the print film, so judge it visually after the controlled wash and record it with photos.

Separate ink, cure and fabric

Ask the factory for the ink system used and the ink supplier's technical data, including the recommended curing conditions. Then ask what the production line actually ran. If production fell outside the supplier's window, under-curing becomes a likely cause. Ink and cure are linked, and the ink maker's data is the reference, not a general rule of thumb.

Then look at where the cracks are. Cracking concentrated where the garment stretches most, such as across the chest of a fitted style, or on a fabric with more stretch, points to a mismatch between the print film's flexibility and the fabric. That can be tested by stretching a printed panel and checking it after the controlled wash.

Agree the test before the next order

For the reorder, add a print-durability check to the specification: wash procedure, cycle count, and the acceptance criterion, for example no cracking visible at a stated viewing condition. Approve a washed print sample as the standard. The care label should match the conditions you tested under, as the FTC Care Labeling Rule requires care instructions to be supportable.

That turns a three-way argument into one documented test that all three parties agreed to.